Several patents teach the use of additional structures to stiffen particular regions of a mattress or mattress core. However, none of these patents offers the features or advantages of the present invention. For example, Higgins U.S. Pat. No. 4,180,877 teaches a mattress having increased firmness in a preselected area on both top and bottom surfaces of the mattress through use of a welded wire grid structure attached to the top and bottom surfaces of the mattress core. The wire grid provides increased firmness over the middle third of the mattress, or alternatively, over the entire mattress surface, but does not offer selective stiffening of other mattress regions.
U.S. Pat. No. 4,122,566 to Yates discloses a spring foundation unit having one or more pairs of inner border members on the top and bottom surfaces of the unit. Each inner border member has side elements extending parallel to opposed sides or ends of the spring foundation unit, and a cross-connecting element interconnecting one end of each of the inner border member side elements to form essentially U-shaped members. Each side element has a free end which is attached to a side or an end of the spring foundation unit. Although the inner border members increase firmness along portions of the mattress sides and midsection, the Yates invention does not enhance firmness along the edges of the mattress, where significant weight may be applied when a person sits on the bed.
Rogovy U.S. Pat. No. 2,724,842 teaches a mattress with independently adjustable spring means on opposite sides of the longitudinal center line of the mattress so that the hardness of the mattress halves may be independently adjusted. The spring means is supported by conventional coil springs and is provided with a crank or other means for adjusting hardness of the spring means. This stiffening device offers increased mattress firmness over a person's whole body, but does not allow for more selective stiffening of particular mattress regions.
U.S. Pat. No. 2,383,157 to Pink teaches an inner closed frame mounted on the flat surface area of the spring system. The frame is located on the surface area so that the springs located within the frame occupy the area upon which a person's greatest weight rests in the normal use of the mattress. A frame is provided on both the top and bottom surfaces of the spring system. In a bed designed for two people, two frames are used side-by-side on each mattress surface. In general, each frame provides a stiffened rectangular ring around each person's torso on the mattress. However, there is no additional support within the interior of each closed frame which is where the greatest weight will rest when a person is lying down on the mattress.
Finally, in U.S. Pat. No. 2,131,071 to Raduns, a mattress is disclosed in which the upper surface is provided with two resiliently suspended and supported platforms situated side-by-side and running lengthwise along the mattress. These platforms consist of either diagonally or laterally and longitudinally arranged strips, wires or springs which are suspended from the periphery of the bed. These platforms increase mattress firmness over the entire body region of a two person mattress, however, the '071 patent does not teach highly selective regions of increased firmness.
Therefore, it is desirable to have a mattress with enhanced firmness in the region where a person typically sits on the mattress with his or her feet on the floor, as well as a simultaneous region of enhanced firmness across the midsection of the mattress where much of a person's weight is supported.